Recently, liquid crystal displays have become as the most powerful displays with which the Braun tube (a cathode ray tube) may be substituted since the liquid crystal displays have an advantage that they are light-weight and driven at low power consumption. In particular, a thin film transistor liquid crystal display (TFT-LCD) driven by a thin film transistor independently drives respective pixels, and therefore the TFT-LCD has been increasingly used in the field of various applications such as notebook computers, wall-mounted TV and the like since the TFT-LCD may display a high-quality moving image due to the very rapid response time of liquid crystal.
In general, a color thin film transistor-liquid crystal display, which is manufactured by disposing linearly polarized components in outer surfaces of two glass substrates in the manufacture of the liquid crystal display, and forming additional anisotropic films on the linearly polarized components, is used to display information by adjusting the capacity of light transmitted from the rear of the liquid crystal display in addition to the reaction of liquid crystal molecules between the glass substrates, and ensure a wide viewing angle through an anisotropic film.
However, when small portable electronic equipments, for example notebook computers, personal digital assistants (PDA), players, mobile phones and the like, are increasingly used in public places for personal purposes, it is necessary to make a viewing angle narrow in consideration of user's private lives. Also, a glare problem may be made serious by external light as the displays are manufactured with a larger scale. In this case, a viewing angle control layer preventing external light from entering the displays is required to enhance the contrast of the displays.
U.S. Pat. No. 6,398,370 discloses a method for manufacturing a film having a function to adjust a viewing angle by forming a pattern in which a black ink layer is vertically aligned in the film in a blind form so as to prevent light from being transmitted at a predetermined viewing angle. However, the technique has disadvantages that the manufacturing process is complicated, and the thickness of the final product is high since the final product is prepared by stacking two films.
U.S. Pat. No. 6,337,111 discloses a thin film and a method for manufacturing the same, wherein the thin film has light absorption anisotropy that is able to easily achieve the attenuation, polarization, scattering and interception of lights comprising laser light and natural light. In the U.S. patent, it is described that an optically anisotropic thin film is produced by forming an orientation film of prescribed mode on a transparent or semitransparent substrate, applying a solution of a dichroic dye in a solvent to the orientation film, and fixing the orientation of the dichroic dye by evaporating the solvent from the dichroic dye solution, wherein the dichroic dye is an azo or anthraquinone dyes, and has liquid crystalline properties and photo- or thermal cross-linking reactive group. However, when a vertically oriented film is formed only of the dichroic dye, the vertically oriented film has problems that its viewing angle is very narrow, which makes it difficult to adjust a viewing angle.
Korean Patent Laid-open Publication No. 2005-0032468 discloses that a film having a narrow viewing angle is prepared by coating a film with a discotic liquid crystal absorbing visible lights. However, the film is difficult to use for the purpose of adjusting a viewing angle since the dichroic dye has a high absorbance.
Korean Patent Laid-open Publication No. 2007-0003185 discloses that a dichroic liquid crystal layer made of mixture of liquid crystal molecules and a dichroic dye is interposed in a liquid crystal display device and dichroic liquid crystals are tilted in an angle range from 0 to 90 in driving the liquid crystal display device in a narrow viewing angle mode. In the case of the patent, it is, however, possible to form a narrow viewing angle in liquid crystal display device by tilting a dichroic dye in respect to a vertical orientation mode when an electrical signal is applied to the dichroic dye.
Japanese Patent Laid-open Publication No. 2005-215435 discloses a viewing angle control member comprising a light-transmissive base substrate; and a viewing angle control layer formed on the base substrate to control the visibility of a subject to be viewed according to the viewing angle. In the patent publication, the viewing angle control layer comprises a dichroic dye and a polymerizable liquid crystal whose molecules are in a rod type, and each of the dichroic dye and the polymerizable liquid crystal has a molecule array fixed in a homeotropic alignment state.
Also, Japanese Patent Laid-open Publication No. 2005-215435 discloses that the viewing angle control member has good visibility to a subject to be viewed in a normal direction, and therefore serves to protect a user's privacy from being exposed to others. However, the use of a non-polymerizable dichroic dye may cause fine phase separation in curing a polymerizable liquid crystal. In this case, when the non-polymerizable dichroic dye is added at a content of 5% or more, the front transmittance and narrow viewing angle characteristics may be deteriorated, and the entire physical properties of the film may be deteriorated due to the aging effect that is spread out of the film when the film is formed and used.
Furthermore, European Patent Application No. 0 608 924 discloses a liquid crystal polymeric film in which liquid crystal molecules are oriented homeotropically, comprising at least one dichroic dye. However, when the liquid crystal is oriented while being mixed in the polymeric film or attached to a side chain of the polymeric film, the entire orientation of the liquid crystal may be worsened, which leads to the deteriorated physical properties of the final product.
Accordingly, the conventional methods actually has problems that a function of adjust a narrow viewing angle is poor, or the durability of the final product is deteriorated, and the manufacturing cost is high.